Recording with an ink-jet technique involves discharging ink from ink discharge orifices that are aligned on a recording head and are substantially orthogonal to the horizontal scanning direction while moving the recording head across a recording medium in the horizontal scanning direction. If timings of the ink discharges are inconsistent, a problem arises that the inconsistency is directly reflected in a recorded image as the recording head horizontally scans, leading to inconsistency in image density. To prevent this inconsistency, an apparatus that generates pulses at regular distances has been conventionally used to perform recording by using the outputs of the apparatus as recording triggers and thereby to suppress the recording inconsistency.
With improvement in image quality, another approach to suppressing the inconsistency in density has been recently taken. As disclosed in Japanese Patent Laid-Open No. 11-192746, this involves generating pulses from pulse outputs multiplied by N in a multiplier circuit and using the multiplied pulses as triggers.
FIGS. 3A and 3B describe control for suppressing the recording inconsistency. Reference heat timings 203 in FIG. 3A are generated from an encoder signal (A) 201 and an encoder signal (B) 202. This reference heat timing signal is a signal for controlling the position of a carriage on which a recording head is mounted. Based on this signal, a heat timing of a first nozzle line arranged on the recording head is determined (204). For the sake of simplicity, in this example, the heat timing of the first nozzle line (204) is controlled as the same timing as the one in the reference heat timings (203). Reference 205 denotes a heat timing of a second nozzle line, reference 206 denotes a heat timing of a third nozzle line, and reference 207 denotes a heat timing of a fourth nozzle line.
The heat timing of the second nozzle line 205 illustrates that it is controlled with a shift by one cycle (T) of the reference heat timings compared to the first nozzle line. The heat timing of the third nozzle line 206 illustrates that there is a timing shift by one cycle (T) and a period (t1) shorter than one cycle (less than one cycle) of the reference heat timings compared to the first nozzle line.
FIG. 3B shows a timing chart in which a cycle (T) of the reference heat timings is divided into 16 periods, wherein a period is defined as t. The timing shift t1 of less than one cycle in FIG. 3A corresponds to a timing 5t in FIG. 3B.
The heat timing of the fourth nozzle line 207 illustrates that there is a timing shift by one cycle (T) and a period (t2) less than one cycle in the negative direction compared to the first nozzle line. In actual control, a shift by one heat timing (cycle T) is generally addressed by shifting pixel data to be output (recorded) rather than shifting the heat timing, whereas a shift of less than one heat timing (period t) is generally addressed by actually shifting the heat timing. In performing such control, controlling the heat timings of the nozzle lines in fractions of a cycle as shown by the hatched pulses can make the heat timings accurately determined. Therefore, controlling in such a manner can provide recording with few misalignments of pixels.
In this example, waveforms of a phase A (201) and a phase B (202) of the encoder signals are always the same and are exactly 90° out of phase with each other for the sake of simplicity. In practice, the phases A and B in FIG. 3A may have different cycle lengths due to eccentricity of a motor or other reasons. In that case, control may include processing such as determining the cycle (T) by dividing a last measured value by four.
The shift amounts in heat timings (cycles T) and in fractions of a heat timing (periods t) are maintained separately for each nozzle line. These values may be factory-preset or may be input by a user based on a result of printed patterns for determining the shift amounts.
In recent years, semiconductor circuits for controlling recording apparatuses are often integrated to reduce the cost of the recording apparatuses. For example, a CPU, a logic circuit, and RAM and so on are integrated into one chip. In this case, the capacity of the RAM mounted on the integrated chip is often reduced under constraints of the chip. The recording apparatuses that use such a chip adopt various control schemes to process data with a small memory capacity.
For example, the amount of image data is reduced or the capacity of the RAM is saved by storing data for the discharge orifice lines (nozzle lines) aligned in the horizontal scanning direction except for data corresponding to distances from an end nozzle line to each of the other nozzle lines.
FIGS. 4A and 4B schematically show the details of saving the memory capacity. In particular, FIG. 4A schematically shows data required when the memory is not saved. In the figure, 410 denotes a carriage, and 401 to 404 denote the first to fourth nozzle lines arranged on the carriage 410. These nozzle lines are spaced apart at a pitch of “d” on the carriage. A recording medium 412 has a recording area 411, in which the carriage 410 scans the recording medium at a constant speed in the horizontal scanning direction and forms an image based on the stored data. Because recording is not performed while the carriage accelerates and decelerates, the nozzle lines cannot record data even if they have the data at areas where the carriage starts and reaches the constant speed and where the carriage drops the speed from the constant speed and stops. Therefore, if the RAM stores a full amount of data for the carriage movement, each nozzle line inevitably has blank image data (null data) indicated by hatching at its left or right end. These hatched portions are unnecessary data.
In the case of FIG. 4A, once any one of the nozzle lines is enabled for recording, other nozzle lines are also enabled for recording. That is, separate enable control is not required for each nozzle line, and this makes the control rule simple. A heat enable signal common to all nozzle lines can be used to read the image data and transfer it to the recording head.
FIG. 4B shows timings of heat enable signals where the amount of the image data is reduced. This is done by storing the data for the discharge orifice lines aligned in the horizontal scanning direction except for data corresponding to distances from an end nozzle line to each of the other nozzle lines (that is, not storing data for the hatched portions in FIG. 4A). In this case, applying a dedicated control signal to each nozzle line eliminates the need to store the unnecessary data in a data storage area. However, the heat enable signals have to be separately controlled for the respective nozzle lines, and this makes the control rule more complicated comparing to the case of FIG. 4A.
Traditionally, the capacity of the RAM has not been so important because an external RAM has been used, so that the control as shown in FIG. 4A has been general. If circuit boards for controlling recording are integrated into one chip as mentioned above, the control as shown in FIG. 4B is adopted because it can save more memory capacity. Since the control as shown in FIG. 4B has been adopted in low-end recording apparatuses, correction in pixels has been enough for the heat timing shifts.
Next, recording buffers used in conventional recording apparatuses will be described. In FIG. 7A, the vertical direction corresponds to the width of a nozzle line. For example, if the nozzle line has 128 nozzles, it has a length for 128 rasters accordingly. The horizontal direction corresponds to the scanning direction of the recording head, and its length corresponds, for example, to 2880 dots (2880 columns). For 360 DPI, it corresponds to 8 inches. The figure shows a buffer 701 storing cyan (C) data, and a buffer 702 storing magenta (M) data. Each buffer stores data for one dot as a shaded portion at a position of 513th column.
When the data is recorded on a recording medium 700 such as recording paper, the shaded portion 703 formed of the cyan (C) dot is recorded at a position of the 513th column (FIG. 7B). Here, if the magenta (M) data has a pixel error (registration error) for one pixel, the shaded portion 704 formed of the magenta dot is recorded at a position of the 514th column. To correct this registration error, the magenta data is read earlier than the cyan data by one pixel.
The “registration” refers to processing by which recording-data decomposed into color components of ink (yellow (Y), magenta (M), cyan (C), and black (B)) is combined into the original color recording data. In the additive process of recording processing, misalignment of the combined colors may occur, which is referred to as a “registration error” (simply called a “regi-error” hereafter). Processing for resolving the regi-error is referred to as “regi-error correction.”
It is essential to efficiently utilize memory areas in that the capacity of memory in recording apparatuses has to be reduced as described above.
Further, to correct regi-errors that occur as described above, it is required to efficiently read image data stored in the memory in combination with the efficient utilization of the memory areas.